To further evaluate the effect of temperature and PMA treatment on persistence trends in river water, a statistical comparison using a multivariate ANOVA was performed between pairs of temperatures (5 and 15°C, 15 and 25°C). Results in Table 2 show that both viable (with PMA) and total (no PMA) cell persistence were significantly affected by temperature, as the calculated Fobserved values for almost all paired comparisons (between each of the two temperatures) exceeded the Fcritical value of 4.75, with the exception of S. enterica and A. butzleri at higher temperatures (between 15 and 25°C). Overall results of the statistical analysis showed that the differences between temperatures were considerably smaller for viable compared with total cells. Although this should be further studied, these results suggest that the effect of temperature on the persistence of bacteria may be overestimated using some methods that cannot differentiate viable and dead cells.

Table 2

F-values determined by two-way ANOVA analysis to test the effect of temperature on pathogen persistence in river water

 Between 5 and 15°C
Between 15 and 25°
Strain+ PMA− PMA+ PMA− PMA
Yersinia enterocolitica 5.62* 62.27* 13.15* 54.40* 
Salmonella enterica 17.09* 33.21* 1.75 13.36* 
Campylobacter jejuni 245.42* 230.44 23.82* 23.40* 
Arcobacter butzleri 115.86* 1166.40* 0.85 24.76* 
 Between 5 and 15°C
Between 15 and 25°
Strain+ PMA− PMA+ PMA− PMA
Yersinia enterocolitica 5.62* 62.27* 13.15* 54.40* 
Salmonella enterica 17.09* 33.21* 1.75 13.36* 
Campylobacter jejuni 245.42* 230.44 23.82* 23.40* 
Arcobacter butzleri 115.86* 1166.40* 0.85 24.76* 

The Fcritical value at α = 0.05 is 4.75, and values that show a significant difference are marked (*).

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